The reforming of petroleum raw materials is an important process for producing useful products. For example, reforming can be used in processes for the separation and upgrading of hydrocarbons for use as a transportation fuel, such as producing a naphtha feedstream and upgrading the octane value of the naphtha in the production of gasoline. Additionally, hydrocarbons in feedstreams from a raw petroleum source may also be utilized the production of desired chemical precursors for use in the production of plastics, detergents and other products. Accordingly, reforming may be used to produce the desired chemical precursors.
The catalytic reforming process is well known in the art. The principal reactions that take place are the dehydrogenation of naphthenes to aromatics, dehydrocyclization of paraffins, isomerization of paraffins and naphthenes, hydrocracking of paraffins to light hydrocarbons, and formation of coke which is deposited on the catalyst. The formation of coke on the catalyst causes the catalyst to gradually lose activity over time. Accordingly, the catalyst requires regeneration and/or replacement. A continuous transfer of catalyst from and to the reactor is highly desirable.
Typically, in such a reactor, a hydrocarbon feedstock and a hydrogen-rich gas are preheated and charged to a reforming zone containing typically two to five reactors in series. The effluent from the first reactor is withdrawn, heated, and passed to the second reactor. The effluent from the second reactor is withdrawn, reheated and passed to the third reactor. The withdrawal and reheating of the effluent continues until the last reactor and is typically referred to as a radial flow. From the last reactor, the effluent is withdrawn and processed further.
The feedstock/partially converted effluent streams are oftentimes passed into the reactor stack via non-reactive sections that are thermally unstable. Catalyst flows downward through the non-reactive sections in conduits so as to avoid contacting the feedstock/partially converted effluent streams. This empty same is required for meeting the hydraulics requirements in some reactors. In other reactors, the space is required for the reactor inspection, maintenance, and repair.
However, within the non-reactive zones preceding, or upstream, of each reactive zones, the compounds in the feed for that reactive zone may undergo undesired non-catalyzed molecular weight reduction transformation. These molecular weight reduction transformation reactions occur in the absence of catalyst and produce less desirable chemicals and lower the production yield of the reactor.
Therefore, it would be desirable to minimize the molecular weight reduction, while maintaining the required space necessary for hydraulics or maintenance.